This invention relates to protective films for information displays.
Optical displays, and especially touch panel displays, typically have an exposed viewing surface made from a thermoplastic film or slab. Commonly-employed thermoplastic polymers have very good optical transparency, dimensional stability and impact resistance, but unfortunately have poor abrasion resistance. The optical displays of devices such as personal digital assistants (xe2x80x9cPDAsxe2x80x9d), cell phones, touch-sensitive screens and removable computer filters are subjected to frequent handling and contact with the user""s face or fingers, styli, jewelry and other objects. For example, facial oils can adversely affect contrast, color saturation or brightness of a cell phone display. The screens of projection televisions and laptop computers are handled less frequently but nonetheless are sometimes touched, scratched or smudged. Consequently, the viewing face of the display is susceptible to scratches, abrasion and smudges arising during routine use. This can cause the display to lose resolution and clarity, and sometimes to become unreadable or inoperative. To protect such displays, protective films or coatings can be employed.
Protective films for PDAs, cellular phones and other display devices are available from many commercial sources including A.R.M. (SECURER(trademark) Screen Protector), CompanionLink Software, Inc. (COMPANIONLINK(trademark) PDA Screen Protector), EC Film (PDA Screen Protector), Fellowes Corporation (WrightRIGHT(trademark) PDA Screen Protector), PerfectData Corporation (SILKYBOARD(trademark) PDA Keyboard and Screen Protector), ROTA Technology Inc. (RT-PDS Screen Protector and RT-MPS Mobile Phone Screen protector), Swann Communications (PDA PLUS(trademark) Screen Protectors), Sanwa Supply Inc. (LCD-PDA Screen Protector) and VSPS (V.S. Protective Shield). Typically these products are sold as single precut sheets of plain plastic film, although some include a textured or tinted surface over at least a portion of the film. Some of the above-mentioned protective films are said to help keep a PDA screen smudge-free. Viewing screen protective devices are also shown in, e.g., U.S. Pat. Nos. 4,907,090 (Ananian); 6,059,628 (Yoo et al.); 6,250,765 (Murakami) and Re. 35,318 (Warman). A touch panel device having a roughened outermost surface is shown in Japanese published patent application (Kokai) No. 2000-020240.
Hardcoats have also been used to protect the face of information displays. These hardcoats typically contain inorganic oxide particles, e.g., silica, of nanometer dimensions dispersed in a binder precursor resin matrix, and sometimes are referred to as xe2x80x9cceramersxe2x80x9d. For example, U.S. Pat. No. 5,104,929 (Bilkadi ""929) describes UV curable ceramer coatings containing colloidal silica particles dispersed in a protic group-substituted ester or amide of an acrylic acid. A ceramer described in Bilkadi ""929 and known as 3M 906 Abrasion Resistant Coating has been used as a hardcoat on signage.
U.S. Pat. Nos. 6,132,861 (Kang et al. ""861), 6,238,798 B1 (Kang et al. ""798) and 6,245,833 B1 (Kang et al. ""833) and Published PCT Application No. WO 99/57185 (Huang et al.) describe ceramer compositions containing blends of colloidal inorganic oxide particles, a curable binder precursor and certain fluorochemical compounds. These compositions provide stain and abrasion resistant hardcoats in a single layer coating.
A transparent stack of anti-graffiti sheets is shown in PCT Published application No. WO 00/24576 (Janssen et al.). The entire stack is applied to a glass or plastic window, signage or a display and the topmost sheet is removed once the sheet has become damaged. The sheets in the stack can include an optional release layer. The release layer is said preferably to comprise a material selected from the group consisting of acrylates, methacrylates, urethanes, polyolefins, silicones, fluorochemicals such as fluorocarbons, and mixtures thereof. In Example 7, 3M 906 Abrasion resistant Coating is employed as an abrasion-resistant release layer atop polycarbonate sheets in the stack. Stacks of removable plastic sheets for use on automotive windows are shown in U.S. Pat. No. 5,002,326 (Westfield et al.) and in Offenlegungsschrift DE 36 37 188 A1 (Altmann et al.).
U.S. Pat. No. 5,851,674 (Pellerite et al.) describes a self-assembling fluorinated silane film that can be applied atop a multilayer antireflective film to provide a coating having antisoiling properties.
U.S. Pat. No. 6,204,350 (Liu et al.) describes curable coating compositions which comprise alkoxysilane containing fluorinated polymers.
Coatings made from 3M 906 Abrasion Resistant coating are susceptible to smudges, staining and marks from pens or pencils. It can be difficult to mix the ingredients in the Kang et al. ""798 and Kang et al. ""833 compositions without experiencing flocculation. Owing to the high cost of the fluorochemical and its use throughout the hardcoat layer, these compositions are also relatively expensive. The Pellerite et al. films have insufficient adhesion to a film made from a ceramer such as 3M 906 Abrasion Resistant Coating.
The present invention provides in one aspect protectors for a display device having an information display area (e.g., a screen), comprising a stack of flexible substantially transparent sheets, the sheets having on one side thereof an adhesive layer and having on the other side thereof a hardcoat layer comprising inorganic oxide particles dispersed in a binder matrix and a low surface energy fluorinated compound, the stack being cut so that the sheets will fit the information display area. The low surface energy fluorinated compound can be blended into the hardcoat layer or can be a separate layer atop the hardcoat layer.
The present invention also provides a method for making information display protectors for electronic devices having an information display area, comprising:
a) applying to one side of a substantially transparent generally planar substrate a curable hardcoat layer comprising inorganic oxide particles dispersed in a free-radically polymerizable binder matrix and a low surface energy fluorinated compound;
b) curing the hardcoat layer;
c) applying to the other side of the substrate an adhesive layer;
d) forming the coated substrate into a stack of sheets; and
e) converting the stack so that the sheets will fit the information display area.
The information display protectors of the invention have very good scratch, smudge and glare resistance and very good durability. The stack of information display protectors can be stored on the display device (e.g., on a PDA or on a PDA cover or case).